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What's in a Lethal Injection ‘Cocktail'? New York Times highlights a rather confused issue.

The latest controversy over the always controversial subject of capital punishment: the drugs used to execute people on death row.

Lawyers for death row inmates in Texas and Arizona have filed challenges to the executions questioning the use of specific drugs in the lethal injection of their clients. (Last week, the Supreme Court stayed the executions for other reasons.)
These challenges have been prompted by a shortage of one of the drugs, sodium thiopental, an anesthetic. The American manufacturer of sodium thiopental, Hospira, recently announced that it would no longer produce the drug, and manufacturers in Europe do not want to supply the drug if it will be used in executions. Some executions have been postponed while states try to sort out the drug situation.
In Texas, which carries out more executions than any other state, the controversy is focused on the proposed switch from sodium thiopental to pentobarbital in a 3-drug cocktail.
What is the difference?
The 2 drugs come from the same family: barbiturates, drugs that depress the central nervous system. So, in general, said Dr. John Dombrowski, director of the Washington Pain Center and a board member of the American Society of Anesthesiologists, “it’s like if you ask me what’s the difference between Johnnie Walker Blue, Black and Red — they’re all scotch.”
But sodium thiopental has been commonly used as an anesthetic in hospitals. Pentobarbital has a few medical uses in humans, but is often used by veterinarians to anesthetize or euthanize animals. It has also been used in physician-assisted suicide in Oregon and in Europe.
When injected into the bloodstream, both drugs “cross the blood-brain barrier very efficiently,” said Dr. Scott Segal, chairman of the department of anesthesiology at Tufts Medical Center in Boston. “They get into brain tissue itself.”
Within the brain tissue, on the surface of the neurons, he said, are receptors that respond to a neurotransmitter called gamma-aminobutyric acid, or GABA.
“GABA is an inhibitory receptor, meaning that stimulation of the GABA receptor reduces firing of neurons,” Dr. Segal said, depressing the brain’s electrical activity.
Both drugs stimulate these GABA receptors.
“All barbiturates put the brain to sleep by slowing down brain function,” said Dr. Mark A. Warner, president of the American Society of Anesthesiologists. “The brain cells that drive the desire to breathe are also suppressed. So any barbiturate, if you give enough of it, somebody quits breathing. Also, if you give enough of it the heart quits pumping as hard and that can cause decreased blood pressure.”
But while the way the drugs work might be similar, the effects are different.
Sodium thiopental is used in hospitals because it “has a relatively fast onset and it doesn’t last long,” Dr. Warner said. “You want a patient to go sleep and wake up pretty quickly.”
Pentobarbital is a long-acting drug.
“If veterinarians are using this, they don’t really care if an animal wakes up faster or not,” Dr. Dombrowski said. “If the dog or cat is still a little sleepy it doesn’t make a difference."
In euthanizing animals, higher doses are used, and “the lethal effect is a cardiovascular effect,” Dr. Segal said, meaning that it stops the heart.
Pentobarbitol is used in hospitals in certain circumstances, like inducing a coma in brain-damaged patients because “that allows the brain to use more energy and oxygen to repair itself,” Dr. Warner said. He said it can also be used to stop seizures in patients for whom other drugs are ineffective.
Opponents of the death penalty object to either drug. Some say thiopental can wear off too quickly, allowing inmates to feel pain.
Others object to using pentobarbital, because it is so infrequently used in humans.
In the three-step cocktail common in executions, a barbiturate is given with pancuronium bromide, a paralyzing drug, and potassium chloride, which induces cardiac arrest. Dr. Segal said all three drugs can have lethal effects.
“I’m not sure anyone knows which drug actually kills someone,” he said.
In fact, one can do the job. Ohio has used both barbiturates by themselves in executions.